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team: avoid race condition in scheduling delayed work 

When team_notify_peers and team_mcast_rejoin are called, they both reset
their respective .count_pending atomic variable. Then when the actual
worker function is executed, the variable is atomically decremented.
This pattern introduces a potential race condition where the
.count_pending rolls over and the worker function keeps rescheduling
until .count_pending decrements to zero again:

THREAD 1                           THREAD 2

========                           ========
team_notify_peers(teamX)
  atomic_set count_pending = 1
  schedule_delayed_work
                                   team_notify_peers(teamX)
                                   atomic_set count_pending = 1
team_notify_peers_work
  atomic_dec_and_test
    count_pending = 0
  (return)
                                   schedule_delayed_work
                                   team_notify_peers_work
                                   atomic_dec_and_test
                                     count_pending = -1
                                   schedule_delayed_work
                                   (repeat until count_pending = 0)

Instead of assigning a new value to .count_pending, use atomic_add to
tack-on the additional desired worker function invocations.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Fixes: fc423ff00d ("team: add peer notification")
Fixes: 492b200efd ("team: add support for sending multicast rejoins")
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Joe Lawrence 2014-10-03 09:58:34 -04:00 committed by David S. Miller
parent 34a419d4e2
commit 47549650ab
1 changed files with 2 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/net/team/team.c
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@ -647,7 +647,7 @@ static void team_notify_peers(struct team *team)
{
if (!team->notify_peers.count || !netif_running(team->dev))
return;
atomic_set(&team->notify_peers.count_pending, team->notify_peers.count);
atomic_add(team->notify_peers.count, &team->notify_peers.count_pending);
schedule_delayed_work(&team->notify_peers.dw, 0);
}
@ -687,7 +687,7 @@ static void team_mcast_rejoin(struct team *team)
{
if (!team->mcast_rejoin.count || !netif_running(team->dev))
return;
atomic_set(&team->mcast_rejoin.count_pending, team->mcast_rejoin.count);
atomic_add(team->mcast_rejoin.count, &team->mcast_rejoin.count_pending);
schedule_delayed_work(&team->mcast_rejoin.dw, 0);
}